Electrically-operated vibratory device



Dec, 30, 1930. M. TROUTON ELECTRICALLY OPERATED VIBRATORYDEVICE Filed Feb. 29, 1928 Patented Dec. 30, 1930 UNITED STATES PATENT oFFIcE MAURICE TROUTON, F BUCKINGHAMSHIRE, ENGLAND, ASSIGNOR TO WIRELESS MUSIC LIMITED, 01 LONDON, ENGLAND ELECTRICALLY-OPERATED VIBRA'IORY DEVICE Application filed February 29, 1928, Serial No. 257,971, and in Great Britain April 1, 1927.

The present invention relates to improvements electrically-operated vibratory devices and more particularly to sound transmitting, reproducing or recording devices of the type 5 in which one member isvcaused to vibrate relatively to another member under the influence of electrically generated forces acting between adjacent surfaces on the respective members or in which electrical oscillations are generated by the relative vibration of two members. I

In the case of an electro-magnetic telephone for example, in which the vibration of a reed of magnetic material produces sounds through the intermediary of a diaphragm which is connected thereto, it has been common practice to anchor the reed at one end and to allow the other, free, end thereof to vibrate above (and towards and away from) the pole tips of a magnet, in response to the 5 ing the magnet or the pole tips thereof. I11

most cases the surface on which the reed is anchored has been parallel with the upper surfaces of the magnet pole tips and suitable adjusting means has been provided for moving said pole tips vertically, so that the normal air gap between the armature portion of the reed and the pole tips can be adjusted to the desired height.

With such an arrangement, when the reed is vibrated the free end or tip of the armature or the portion thereof furthest from the anchorage will approach closer to the magnet pole surface than the other end of said armature portion. The magnetic pull will also increase as the armature approaches the magnet poles.

It will also be understood that the magnetic pull will only be uniformly distributed over the surface of the armature when the latter is parallel to the pole surfaces. If the tip of the armature is closer to the pole surface than the heel (or the end of the armature portion of the reed nearer the anchorage) the magnetic lines of force will tend to concentrate toward the tip and, conse-.

quently, the point of action of the resultant magnetic force will be closer to the tip than to the heel of the armature.

In the case assumed above, therefore, the center of magnetic force will move away from the reed anchorage and toward the tip of the armature as the latter approaches the magnet poles, and, therefore, the arm of the moment of the magnetic force will increase as the armature approaches the poles.

A simple reed obeys Hooks law over the small displacements met with in sound reproduction, that is to say, there is a linear relation between the displacement of a point on the reed and the mechanical force applied at'that point. The magnetic pull, however, changes too rapidly close to the magnet, compared with the changes which take place further from the poles, to be balanced by a simple spring and, in addition to this, whenthe tlp of the armature is allowed to approach closer to the poles than the heel, the arm or radius about which the magnetic pull acts also increases as the armature approaches the poles. Since the displacement of the armature is dependent, not upon the magnetic pull, but on the moment of this pull, the relation between the current passed around the coils, surrounding the pole tips and the resulting displacement will be far from linear.

One of the objects of the present invention is to provide an electro-magnetic vibratory device of simple form, in which substantially maximum sensitivity is obtained while the relation between applied current.

and resulting displacement is much more nearly linear than has been the case with constructions heretofore proposed.

A further object of the invention is to provide an electro-magnetic vibratory device which has the desired qualities of sensitivity and linearity, and in which the mechanical restoring force applied to the armature is in the form of simple spring, that is to say, a construction which will obey Hooks law.

The invention will be further described with reference to the accompanying drawing, in which:

Figure 1 is a plan of an embodiment of the invention.

Figure 2 is a transverse vertical section substantially on the line 22 of Figure 1.

Figure 3 is an elevation of the parts shown in Figures 1 and 2.

Figure 4: is a transverse vertical section similar to Figure 2, but showing the relation of the parts when the magnetic force is at zero and when the magnet poles are retracted from the position shown in Fig. 2 into a working position.

Figure 5 is a diagrammatic View.

Figures 6 and 7 are, respectively, a plan and vertical cross section (similar to Figures 1 and 2) of a different embodiment.

Referring particularly to Figures 1 to 4 of the drawings, a designates a pillar rising from a base I) and having a flat upper surface 0 to which is secured, as by screws (Z, a reed n.

As shown, the reed n projects forward from its support a over the pole pieces 9 of a U-shaped permanent magnet f. Preferably, as shown, the pole pieces 9 are of lam inated form and separated by an air gap 70, which, as shown in Figure 3, is beneath the reed a.

Each pole g is surrounded by an electric coil h.

In the following description that portion of the vibratory member or reed n, which lies over and cooperates with the magnet pole or poles 9 will be referred to as the armature, and the end of such armature nearest the support a will be designated the heel thereof, while the other, or free end is termed the toe or tip.

The magnet f is supported between arms 2' that extend rearward and support pivot screws j having suitable bearin s in lugs e projecting forward from the reed supporting pillar a.

The magnet is thus pivotally supported to rock about the axis of the bearings of the screws on the base or supporting member and an adjusting screw Z is provided for moving the magnet bodily about such axis.

Springs 722. rising from the base 6 bear against the magnet f and cooperate with the screw Z to retain the magne in any desired adjusted position.

To the armature portion of the reed n is secured a rod or stem 00, the other end of which is connected to a diaphragm, not shown, as is customary.

The parts are so related that normally, or when the magnet is deenergized, the air gap between the armature and pole pieces 9 will be of angular form. That is, the cooperating surfaces of the armature and pole pieces will be out of parallelism, being spaced further adjacent the tip or toe of the armature than adjacent the heel thereof.

It will be evident that the active part or armature section of the reed n can be regarded, with a considerable degree of accuracy, as rotating or vibrating about a relatively lixed imaginary axis located in advance of the supportor pillar a.

In the embodiment of the invention illustrated in Figures 1 to 4, this axis 0 is substantially coincident with the axis about which the magnet is adjustable, as before described, and located between the rear edges of the pole pieces 9 and the reed support 0.

Extensive experience has shown that if the armature portion of the reed n is so stiff that it can be assumed to remain straight while vibrating, if the magnetic forces be assumed to act at the center of said armature portion, if the reed a be straig it when the magnetic force is zero, and if the angle of deflection of the armature when the magnet is energized is small, then the correct position for the axis 0, in order that the armature may, for all adjustments (within wide limits) contact with the magnet pole surfaces evenly throughout said surfaces, is represented by the equation:

where r is the distance between the axis and the nearer edge of the pole pieces, Z the distance between the reed support a and the nearer edge of the magnet pole pieces and p represents the width of the pole piece (see Figure 5). This is equivalent to saying that, with the above assumptions, the armature portion of the reed in vibrating moves in the arc of a circle having the radius 1".

It will be understood that the total amplitude of movement of an armature, such as before described, when used to actuate the diaphragm of a loud speaker is extremely small, and that, therefore the desired relative positions of the parts in working condition cannot be indicated with accuracy in drawings of the size herein referred to.

As shown in Figures 2 and 4, the length of he surface of the pole pieces g, which cooperate with the armature portion of the reed n measured in a direction radial to the axis is preferably at least as as the distance between the heel of the armature (the right hand edge of the pole pieces 9 in Figures 2 and 4) and the axis 0 so that the change in distribution of magnetic force in the air gap which is produced by change in the relative inclination and distance between the cooperating surfaces of the magnet poles and the armature may be effective in producing a substantially linear relation between applied current and resulting displacement of the armature.

In another form of loud speaker driving element, the vibrating member projects at right angles from a cross bar, which is preferably of rectangular cross section. The

two ends of the cross bar are firmly clamped. The portion of the vibratory member between the cross bar and the heel of the arm ature is stiffened by means of suitable webs and the remainder is left relatively flexible and constitutes the armature. When the armature is in position in the magnetic field the cross bar is subjected to torsion and this provides the requisite restoring force. In this case the axis of rotation of the armature is on a line passing through the centre of the cross bar and the magnets are pivoted for adjustment purposes about an axis situated substantially at the same distance from the nearer edge of their pole surfaces as the axis of rotation of the armature.

The embodiment of the invention just referred to is illustrated in Figures 6 and 7, referring to which it will be seen that the armature or vibrating member t, which is connected with the diaphragm actuating rod :0, projects at substantially right angles from a cross bar u, which is enlarged at its ends and secured by suitable screws o to pillars on the supporting frame. As previously described, and as shown in the drawing, the cross bar a is preferably of rectangular form in cross section and the connect-ion between it and the armature t is stiffened as at It will be understood that although the invitation has been described in detail as applied to a loud speaker driving element it is not so limited. In particular it is equally applicable to devices for converting mechanical vibrations into corresponding electrical vibrations.

I claim:

1.'An electrical vibratory device comprising a magnet pole, a supporting bar clamped at both ends, and an armature of magnetic material projecting from said supporting bar, the co-operating surfaces upon the magnet pole and armature being inclined to one another when the magnetic force between said surfaces is reduced to Zero, the inclination being such that if the armature is displaced to an extent which brings the co-operating surfaces into contact, the angle between said co-operating surfaces is less than it Would be if no relativeinclination were provided at zero magnetic force.

2. An electrical vibratory device comprising a magnet pole, a supporting bar clamped at both ends, a still member projecting from said bar, and a relatively flex ble armature projecting from said stiff member past the magnet pole, the co-operating surfaces upon the magnet pole and armature being inclined to one another when the magnetic force between said surfaces is reduced to zero.

3. An electrical vibratory device comprising a pair of magnet poles, a supporting bar clamped at both ends, and an armature of magnetic material projecting from said supporting bar over said magnet poles and adapted to co-operatetherewith. I

4. An electrical vibratory device comprising a pair of magnet poles, a supportingbar clamped at both ends, a stilf member projecting from said supporting bar, and a relatively flexible armature of magnetic material projecting from said stifl member over said magnet poles and adapted to co-operate therewith. I

5. An electrical vibratory device comprising a magnet pole, an armature adapted to vibrate towards and away from the magnet pole and to change its inclination relatively to said magnet pole during vibration, and means for adjusting simultaneously the inclination andthe mean distance between the magnet pole and armature when in its position of rest, said inclination being adj ustable in such a direction as to decrease the angle between the armature and the magnet pole when in'closest proximity during working.

6. An electrical vibratory device comprising a magnet pole, an armature adapted to vibrate towards and away from said magnet pole about an axis, and means for rotating the magnet pole about an axis lying at substantially the samerdistance from said magnet pole as the first named axis.

7. An electrical vibratory device comprising a magnet pole and an armature of magnetic material mounted for vibrationabout an axis and adapted to cooperate with and to vibrate towards and away from a surface of said magnet pole, the length of the cooperating surfaces of said armature and said magnet pole in a direction normal to said axis being at least as great as the distance of the heel of said armature from said axis, the toe of said armature being situated further from said magnet pole surface than the heel of said armature in the position of rest of said armature.

8. An electrical vibratory device comprising a pair of magnet poles, a supporting bar clamped at both ends, an armature of magnetic material projecting from said supporting bar over said magnet poles, the length of the cooperating surfaces of the armature and magnet poles being at least as great as the distance of the nearer end of said cooperating surfaces from said supporting bar.

9. An electrical vibratory device comprising a pair of magnet poles, a supporting bar clamped at both ends, a stiff member projecting from said supporting bar, a relatively flexible armature of magnetic material projecting from said stiff member over said magnet poles, and cooperating surfaces upon said armature and said magnet poles, the length of said cooperating surfaces in a direction normal to said supportin bar being at least as great as the length of said stiff member measured in the same direction.

10. An electrical vibratory device, comprising a base, a magnet pole rotatably mounted upon said base, and a vibratory member mounted upon said base and adapted to vibrate rotationally towards and from said magnet pole.

11. An electrical vibratory device, comprising a base, a magnet pole rotatably mounted upon said base, and a vibratory member mounted upon said base and adapt ed to Vibrate rotationally towards and from said magnet pole, the axes of rotation of said magnet pole and said member being substan tially equidistant from said magnet pole.

12. An electrical vibratory device, comprising a base, a magnet pole rotatably mounted upon said base, and a vibratory member mounted upon said base and adapted to vibrate rotationally towards and from said magnet pole, the axes of rotation of said magnet pole and said member being substantially coincident.

In testimony whereof I have signed my name to this specification.

MAURICE TROUTON. 

